In digital broadcasting, for example, in order to prevent a pay content from being watched or listened to in an unauthorized manner, it is often the case that a transmitting side performs encryption processing on content data and then transmits the data. In order to watch or listen to the thus encrypted content, generally, a receiving side needs to perform a decryption processing in accordance with a predetermined method with a key given by the transmitting side.
In order to make a method for decrypting such encrypted content in the form of a black box and to accommodate cases in which security based on encryption is broken with an update of an external module alone, instead of the entire receiver, there is a system in which decryption processing is performed by an external module provided outside the receiver (see Patent Document 1, for example).
FIG. 9 shows a conventional structural example of a digital broadcast receiver 1 using an external module 12. As shown in FIG. 9, the digital broadcast receiver 1 comprises: an input unit 10 for receiving a received broadcast wave; a demodulation unit 11 for demodulating the broadcast wave; an external module 12; an external module I/F (Interface) 13 for connecting the receiver 1 to the external module 12; a decoding unit 14 for extracting necessary information containing a target content from the received signal; an output unit 15 for outputting actual video/audio; a control unit 16 for controlling the entire receiver 1; and a user I/F 17 for transmitting and receiving information to/from a user.
Based on the digital broadcast receiver 1, first, an RF (Radio Frequency) signal received by an external antenna or the like is inputted to the input unit 10, necessary information is obtained from the control unit 16 so as to obtain a desired content designated by the user I/F 17, a target channel is demodulated by the demodulation unit 11, and a TS (Transport Stream) containing the desired content is extracted.
Next, the TS that has passed through the external module 12 is obtained via the external module I/F 13. At this point, since the external module 12 performs decryption processing on the encrypted content designated by the control unit 16, necessary information, such as the TS inputted from the external module I/F 13 or a key for decryption via the control unit 16, is obtained. Next, another encryption processing is performed on the decrypted target content, and the content is then outputted to the external module I/F 13. Further, key information for decryption is transmitted to the control unit 16.
The decoding unit 14 performs decryption processing and the decoding of the TS by obtaining the key information from the control unit 16 and channel selection information for extracting the target content from the TS, and the output unit 15 outputs video/audio. Further, information such as a program list obtained from the TS in the decoding unit 14 is transmitted to the control unit 16.    Patent Document 1: JP Patent Publication (Kokai) No. 2002-312314 A